Hydrodynamic coefficients for roll oscillation
 

I want to simulate forced roll oscillation with 2D rectangular structure with motion: 0.05*sin(0.4*t). How to obtain the damping coefficient and added mass(i.e. b44 and a44). I purely measured the moment and fit the curve into a function like f=Asinwt+Bcoswt+C, however the B value is incorrect.